International Patent Publication No. WO 94/15223 describes a magnetizing device for providing a predetermined magnetization distribution.
A dependence of the electric resistance on the intensity and direction of a magnetic field permeating a material layer may be manifested in layers of ferromagnetic transition metals such as Ni, Fe or Co and their alloys. The effect that occurs with such layers is called anisotropic magnetoresistance "AMR" or anisotropic magneto-resistive effect. The anisotropic magneto-resistive effect is based physically on the different scattering cross sections of electrons with different spin and on the spin polarity of the D band. The electrons are referred to as majority or minority electrons respectively. For corresponding magneto-resistive sensors, a thin film of such a magneto-resistive material is generally provided with magnetization in the plane of the layer. The change in resistance with the rotation of the magnetization with regard to the direction of a current flowing through the magneto-resistive material can amount to several percent of the normal isotropic (=ohmic) resistance.
Furthermore, for some time there have been known magneto-resistive multi-layer systems which contain a plurality of ferromagnetic layers arranged in a stack and separated from each other by metal interlayers, with the magnetization of each layer in the plane of the layer. The chosen thickness of each individual layer is much smaller than the mean free path length of the conduction electrons. In addition to the above-mentioned anisotropic magneto-resistive effect, AMR, such multiple-layer systems may also manifest a giant magneto-resistive effect or giant magneto-resistance, GMR (see, for example, European Patent No. 483,373). The GMR effect is based on the difference in scattering of the majority and minority conduction electrons at the interfaces between the ferromagnetic layers and the adjacent interlayers and on the scattering effects within the layers, in particular when using alloys. The GMR effect is an isotropic effect. The GMR effect can be much greater than the anisotropic effect, AMR, and may assume values up to 70% of the regular isotropic resistance. In corresponding multi-layer systems having a GMR effect, neighboring metallic magnetic layers are at first oppositely magnetized, with one bias layer or bias layer part being magnetically harder than a measurement layer. Under the influence of an external magnetic field, the initial antiparallel orientation of the magnetizations may then be converted to a parallel orientation. This fact is utilized with appropriate magnetic field sensors.
With such magneto-resistive sensor elements with a bias layer part, the required fixed orientation direction of the magnetizations in the respective bias layer part is generally set by introducing the sensor element into a magnetic field of sufficient field strength generated by an electromagnet. If several sensor elements are to be suitably magnetized at the same time for technical manufacturing reasons, this is possible in only a single direction, namely in the direction determined by the field of the magnet.